Takayuki-san,
I also get the red error message when trying to send the email.
This error only occured after updating to the newest version of contact form 7 and also to wordpress 4.6 this morning
It worked fine for months before under the previous versions of cf7 and wp.
Can you please check.
This seems to be an issue with on plugin/wp side and not on the user setup side.
Arigat?!
Dominik